I'd say it's because Lawrie quasi worships Esther. Lawrie is Nick's mirror image but notably lacking in all the qualities - stoicism, team playing, good eggishness - that she so admires in Nicola. Plus, precisely the fact that Esther sees some of the aspects of herself she despises in Lawrie, cowardice for example. The double whammy's enough to provoke her to speak out,